With preliminary investigations under way, experts from the Ministry of Land and Resources explained four causes of the deadly mudslides that hit Zhouqu County, Gansu Province, on the morning of August 8.
The local topography and special geological structure of Zhouqu was one of the key reasons leading to the disaster. Experts believe that the lithology of the mountainous zone around Zhouqu County was soft and easily broken after serious weathering, and thus prone to geological disasters such as landslides and collapse.
Another factor was the 8.0-magnitude Wenchuan earthquake that occurred on May 12, 2008. Zhouqu County was one of the worst hit zones in the Wenchuan earthquake, which loosened the mountain rocks around Zhouqu and made them easier to break. The loose terrain caused by an earthquake usually requires three to five years to recover, but it has only been a little more than two years.
Third, the continual drought in Zhouqu that lasted from late last year until the first half of this year resulted in the disintegration of rocks. Parts of the mountains and cracks in the rocks were exposed and easily permeated by rainwater, which led to mudslides.
Fourth, the heavy rain on the night of August 7 in the mountainous region northeast of Zhouqu lasted for 40 minutes. The amount of rainfall reached more than 90 millimeters, which caused landslides and triggered the disaster.
Experts and workers from the Ministry of Land and Resources are currently investigating the hidden dangers of geological disaster in this area to prevent secondary disasters from occurring.